Nearly every airbag, in particular every motor vehicle front impact airbag, includes a ventilation device through which inflation gas can escape from the airbag internal gas space—hereinafter called the first gas space—for restraint of the person to be protected. The first gas space is enclosed by the outer casing of the airbag, so that kinetic energy of the person to be protected is dissipated and the person to be protected does not simply rebound from the airbag casing of the airbag. In the simplest case such a ventilation device is simply a vent opening, in particular a vent opening in the airbag casing.
In order to take into account different accident situations and/or the weight of the person to be protected, control devices for influencing the shape of the airbag or the pressure in the gas space are known in the prior art. If the shape of the airbag is to be controlled, a releasable catch strap may be provided as a part of the control device. Furthermore, adaptive ventilation devices are known, which in addition to the vent opening include a throttle element, which in a first state throttles the gas flow through the vent opening more intensely than in a second state. Generally the first state is the throttled, or even fully closed state, and the second state is the less-throttled, for example, completely open state.
U.S. Pat. No. 6,648,371 B2 shows an example of an active control device wherein a pyrotechnically functioning actuator is described as part of the control device. Here the first end of a strap is connected to the throttle element and the second end of this strap to a bolt of the actuator. The actuator is thereby held, in particular, on the housing base of the airbag module. As long as the actuator is not actuated, the throttle element is thus connected to the housing base via the strap. In the event of a completely expanded airbag casing, the strap comes into a taut state, which holds the throttle element in its first state. If the actuator is actuated, then the bolts or fasteners that hold the second end of the strap are jettisoned by a pyrotechnic charge, the strap loses its tension, and the throttle element transitions into its second, namely its unthrottled (or less throttled) state. In principle this technology functions very well, but has the disadvantage that parts, such as, for example, the bolts, can fly about inside the gas space of the airbag casing, and that hot gases are created inside the airbag casing due to the pyrotechnic charge. Furthermore the pyrotechnic charge feeds additional gas into the gas space of the airbag casing, which is not always desired.
WO 2014/001317 A1 shows a similarly functioning actuator. Here an ignition capsule is surrounded by a hose. The end (usually upper end) of the hose facing away from the actuator is closed by a tear seam. This tear seam also holds the second end of a strap. If the ignition capsule is ignited due to an electrical signal, the tear seam tears, whereby the initially closed end of the hose opens and the second end of the strap is released. The advantage here is that no bolts or the like can fly about in the interior of the airbag. However, here the gas of the ignition capsule is also fed into the gas space of the airbag.
The generic device described by DE 10 2005 039 418 B4 proposes an airbag module including an adaptive ventilation device, wherein the control device includes a “small airbag module inside the airbag module” having a casing (second casing) and a gas source. Here the throttle element is influenceable by the second casing. The casing of this second airbag—designated hereinafter as the second casing—encloses a second gas space which can be filled by the gas source configured in particular as an ignition capsule. If this happens, then the second casing filled with gas withdraws the throttle element in the form of a cloth away from the vent opening so that the ventilation device transitions into its second, unthrottled state. It is advantageous here in particular that the gas generated by the ignition capsule remains in a second gas space. It is disadvantageous here that the second casing and vent opening must be directly adjacent to each other, which is often very difficult to realize. In particular it is scarcely possible to dispose the vent opening in the airbag casing in such a manner.